Fix an overheating buick rendezvous 2002. Truly overheated once, then had the radiator flushed and replaced, along with thermostat (twice) and water pump. Now, the computer indicates it is overheating

Truly overheated once, then had the radiator flushed and replaced, along with thermostat (twice) and water pump. Now, the computer indicates it is overheating, but it actually isn't! Because the overheating sensor on the computer comes on, i cannot drive more than 20mph. Please help!

You have a needle in a haystack because so many things can cause your problem. I am leaning toward the main computer - which you can replace yourself for around $300. There are companies on the internet that will send you your pre-programmed computer, you have to supply your VIN number. Like many internet companies I always recommend that you are careful in your selection. Be careful to find a reliable company and call them on the phone to make sure they are a real company. If they do not have a phone number - find a different company.

Here are a couple things to try first:
1) Coolant sensor - but this usually makes your car run really poor because it can change the gas/air ratio. If your car is running great other than the overheating sensor - then this probably is not the problem. But worth checking.

2) Serpentine Belt - sometimes when you change the serpentine belt you can put it back on the pulleys out of order. Your car can run great but can cause overheating especially if you have the water pump turning backwards. Since you had the water pump changed you might just take a look at the belt to make sure it is wound correctly. There should be a sticker under the hood.

Before I replaced the computer, I'd make sure the coolant pump was working. I've replaced coolant pumps in older vehicles that had no blades left on the impeller. Also, make sure your cooling fans are coming on and that your thermostat is not installed backwards.

You need to do a diagnostic scan as soon as the 'overheating' light comes on. This should give the mechanic a place to start with his troubleshooting. Sounds to me like the coolant sensor(s) were damaged when your vehicle overheated.

Over heating may damage the coolant temperature sensor and cause the light to come on. when the sensor fails the engine is slow to start and there is a strong odor of gasoline. turn it off and it starts normal the second time.

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Check the radiator cap first, pressure test the cooling system next,, see where the leak is if you have one,, check the electronic fan switch and relay,, ,,, after that it would be the thermostat, check to see if the upper radiator hose gets hot before it overheats,, if not the thermostat may be stuck shut,,, good luck, and of course be careful if a hose blows or cap is bad you can get scalded by the hot water ,, it can be over 220 * f

they should be even temp. check for low fluid level in radiator, may even have a bad thermostat. sorry i can't be more specific, is the car overheating at all? is engine fan on when engine at operating temp? is there any fluid leaking into the passenger compartment? if so, please repost your question. thank you for choosing fixya.com

If the top hose is hot and the bottom is cold, your definitely not getting circulation. You,ve already done alot of work to this vehicle so you have pretty much answered your own question. About the only thing left is the heater core. Of course, I dont want to be the one to tell you it is definitely the heater core because obviously I am not looking at the vehicle. But If i was a betting man, thats where my money would be.

I recommend flushing the radiator thoroughly if not done recently. there seems to be some sort of blockage in the radiator at this time. if you get lots of metal fragments that are flushed out during this flush, i will then recommend a rebuild on the radiator or replacement of the radiator. make sure the cooling fans are cycling on time as well.